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Multi-wavelength observations from various solar missions have revealed the dynamic nature of the solar corona. The work presented in this thesis represents a contribution towards understanding some of the physical mechanisms that drive the activity observed in the corona and out into the heliosphere. In particular, the role of reconnection in active region (AR) outflows and AR-coronal hole (CH) interactions using observations of the associated plasma flow signatures and their relationship to the underlying magnetic field topology is examined. Persistent outflows discovered by Hinode EUV Imaging Spectrometer (EIS) occur at the boundary of all ARs over monopolar magnetic regions. It is demonstrated that the outflows originate from specific locations of the magnetic topology where field lines display strong gradients of magnetic connectivity, namely quasi-separatrix layers (QSLs). Magnetic reconnection at QSLs is shown to be a viable mechanism for driving AR outflows which are likely sources of the slow solar wind. Observational signatures and consequences of interchange reconnection (IR) are identified and analyzed in a number of solar configurations. Jet light curves of several emission lines show a post-jet enhancement in cooler coronal lines which has not been previously observed. In the case of emerging flux near a CH, it is shown that closed loops forming between the AR and CH leads to the retreat of the CH and a dimming of the corona in the vicinity of the like-polarity region. A filament eruption and coronal mass ejection (CME) from an AR inside a CH are observed from the solar disk into the heliosphere. An anemone structure of the erupting AR and the passage in-situ of an interplanetary CME (ICME) with open magnetic topology are interpreted to be a direct result of IR. Plasma flows resulting from the interaction between an AR embedded in a CH observed by Hinode EIS are investigated. Velocity profiles of hotter coronal lines reveal intensification in outflow velocities prior to a CME. The AR's plasma flows are compared with 3D magnetohydrodynamic (MHD) numerical simulations which show that expansion of AR loops drives outflows along the neighboring CH field. The intensification of outflows observed prior to the CME is likely to result from the expansion of a flux rope containing a filament further compressing the neighboring CH field.
A thorough introduction to solar physics based on recent spacecraft observations. The author introduces the solar corona and sets it in the context of basic plasma physics before moving on to discuss plasma instabilities and plasma heating processes. The latest results on coronal heating and radiation are presented. Spectacular phenomena such as solar flares and coronal mass ejections are described in detail, together with their potential effects on the Earth.
Proceedings of the Monterey Workshop, held in Monterey, California, August 1999
Starting in 1995 numerical modeling of the Earth’s dynamo has ourished with remarkable success. Direct numerical simulation of convection-driven MHD- ow in a rotating spherical shell show magnetic elds that resemble the geomagnetic eld in many respects: they are dominated by the axial dipole of approximately the right strength, they show spatial power spectra similar to that of Earth, and the magnetic eld morphology and the temporal var- tion of the eld resembles that of the geomagnetic eld (Christensen and Wicht 2007). Some models show stochastic dipole reversals whose details agree with what has been inferred from paleomagnetic data (Glatzmaier and Roberts 1995; Kutzner and Christensen 2002; Wicht 2005). While these models represent direct numerical simulations of the fundamental MHD equations without parameterized induction effects, they do not match actual pla- tary conditions in a number of respects. Speci cally, they rotate too slowly, are much less turbulent, and use a viscosity and thermal diffusivity that is far too large in comparison to magnetic diffusivity. Because of these discrepancies, the success of geodynamo models may seem surprising. In order to better understand the extent to which the models are applicable to planetary dynamos, scaling laws that relate basic properties of the dynamo to the fundamental control parameters play an important role. In recent years rst attempts have been made to derive such scaling laws from a set of numerical simulations that span the accessible parameter space (Christensen and Tilgner 2004; Christensen and Aubert 2006).
Informal discussions in 1977 among a number of scientists asso ciated with solar and interplanetary physics revealed a need for a dialogue between the two often-divergent groups. It was clear that the latter group was dependent essentially on the sun for its raison d'etre. On the other hand it was also clear that the former group could benefit in its search for insight vis-a-vis solar activity by looking beyond the shell of the inner corona. Needless to add that the combined solar/interplanetary topic is relevant to astrophysics when one considers stellar winds and binary star flows. It was felt, there fore, that a symposium was essential to bring together, for the first time, leading solar and interplanetary physicists from the interna tional community to discuss and record herein their own research. The fundamental physical processes underlying our own capricious star's activity can be understood only by the coupling of solar and interplan etary topics in an intimate observational and theoretical structure. This book, intended for active research scientists and advanced grad uate students, is an important step in this direction. The background of solar and interplanetary dynamics is provided in Part I (The Life History of Coronal Structures and Fields) and Part II (Coronal and Interplanetary Responses to Long Time Scale Phenomena).
This report covers technical progress during the third year of the NASA Space Physics Theory contract "The Structure and Dynamics of the Solar Corona," between NASA and Science Applications International Corporation, and covers the period June 16, 1998 to August 15, 1999. This is also the final report for this contract. Under this contract SAIC, the University of California, Irvine (UCI), and the Jet Propulsion Laboratory (JPL), have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD model. During the three-year duration of this contract we have published 49 articles in the scientific literature. These publications are listed in Section 3 of this report. In the Appendix we have attached reprints of selected articles. We summarize our progress during the third year of the contract. Full descriptions of our work can be found in the cited publications, a few of which are attached to this report.Mikic, ZoranGoddard Space Flight CenterMAGNETOHYDRODYNAMICS; MATHEMATICAL MODELS; SOLAR CORONA; HELIOSPHERE; SUN; THREE DIMENSIONAL MODELS; MAGNETIC FIELDS; SOLAR WIND VELOCITY; KINETIC ENERGY; SOLAR MAGNETIC FIELD
This volume is dedicated to the Solar Dynamics Observatory (SDO), which was launched 11 February 2010. The articles focus on the spacecraft and its instruments: the Atmospheric Imaging Assembly (AIA), the Extreme Ultraviolet Variability Experiment (EVE), and the Helioseismic and Magnetic Imager (HMI). Articles within also describe calibration results and data processing pipelines that are critical to understanding the data and products, concluding with a description of the successful Education and Public Outreach activities. This book is geared towards anyone interested in using the unprecedented data from SDO, whether for fundamental heliophysics research, space weather modeling and forecasting, or educational purposes. Previously published in Solar Physics journal, Vol. 275/1-2, 2012. Selected articles in this book are published open access under a CC BY-NC 2.5 license at link.springer.com. For further details, please see the license information in the chapters.